The invention relates to a method for checking a ring optical network line for data transmission between a plurality of network subscribers in a motor vehicle.
Apart from the known CAN networks for signal transmission, it is known for a network in which the data are transmitted optically to be provided in motor vehicles. This network is constructed as a ring and connects a radio, CD changer, sound amplifier, telephone, mobile telephone and voice control system via an optical databus (D2B).
In contrast to previous asynchronous, that is to say event-controlled, data transmission as in the case of the CAN bus, such communication and information systems require synchronous data transmission at higher Baud rates, which can be transmitted using optical signals.
For example, as a network subscriber, the radio can carry out the master function and at the same time be used as a gateway to the internal bus and diagnostic system. The CAN-B interface allows information from the D2B system to be transmitted to other systems and, conversely, data to be transmitted from the vehicle to the D2B system. Particularly intensive interchange takes place between a combination instrument and the network subscriber having the master function, since the D2B components can also be controlled via the steering wheel, and information can be displayed via the combination instrument display.
All the audio signals, such as music or speech, are initially transmitted in digital form from the component which produces them via the D2B bus either to the network subscriber having the master function or, possibly, to the sound amplifier, where they are converted into an analogue signal and are reproduced via the vehicle loudspeakers. If a telephone system is installed in a vehicle, this has the advantage that there is no need to fit any additional loudspeakers for hands-free operation.
In contrast to conventional vehicle networking, the system components are not linked to one another in a bus, tree or star structure, but in a ring structure. This means that each ring subscriber receives modulated light via the receiving device, carries out signal preprocessing, and then passes on the signal via the optical output. The advantage in this case is that the ring may have any desired number of components added to it, since the maximum optical power is available at the output of each appliance. Since the data are transmitted optically, this is always done unidirectionally, that is to say only in one direction. Optical transmission advantageously allows problems relating to EMC to be avoided.
The operation of such a ring optical network line is described in detail, for example, in VDI Reports No. 1415, entitled Elektronik im Kraftfahrzeug, Tagung Baden-Baden 8 and 9 October 1998=Electronic systems for vehicles/VDI-Gesellschaft Fahrzeug- und Verkehrstechnik, Dxc3xcsseldorf: VDI Verlag, 1998 (VDI Reports; 1415) ISBN 3-18-091415-7.
Furthermore, U.S. Pat. No. 4,930,049 discloses an arrangement in which both an electrical control line and an optical control line are arranged in a star arrangement in a motor vehicle. This allows the components in the vehicle to be actuated either by means of an electrical control signal or by means of an optical control signal.
The object of the present invention is to propose a method and an apparatus in order to allow such an optical network line to be checked for possible faults.
A method according to the invention checks a ring optical network line for data transmission between a plurality of network subscribers in a motor vehicle, wherein one network subscriber carries out a master function, in that apart from the optical network line there is a further communication line which has a star structure and in which the network subscriber having the master function is arranged in the centre of the star structure and is connected directly via the communication line to every other network subscriber, wherein the optical network line is checked by the network subscriber having the master function outputting a start signal to the individual network subscribers via the communication line in a first test step at the start of operation of the optical network line, wherein the individual network subscribers acknowledge the start signal for the network subscriber having the master function via the communication line, wherein, in a second test step after the start signal, the network subscriber having the master function outputs an initialization signal via the optical network line, wherein correct operation of the ring optical network line is identified if the network subscriber having the master function receives a signal which corresponds to a nominal signal via the optical network line within a predetermined time interval.
Thus, first of all, it is advantageously possible to test whether all the network subscribers have a reliable electrical power supply and whether the connection can be set up via the communication line. In the next step, it is then possible to check whether communication can take place via the optical ring line once the other fault sources have been excluded.
The nominal signal may in this case correspond to the initialization signal itself. Thus, in this case and in this test step, the signal is just passed on by the individual network subscribers (possibly amplified) as it was received. It is likewise possible to use the individual network subscribers to change the signal in a characteristic manner, so that correct operation of the individual network subscribers can furthermore be checked.
In general, when interruptions occur in bus systems having a ring structure (for example D2B OPTICAL), the entire data flow breaks down. This leads to failure of all the systems on the bus. This now results in the problem that, in contrast to multi-master bus systems (for example CAN), the individual controllers can no longer respond in order to diagnose the fault via the ring optical network line. The present invention thus advantageously allows the location of the fault which may have occurred to be found with comparatively little effort.
In an embodiment of the invention method, a disturbance in the voltage supply to a network subscriber or an interruption in the connection via the communication line from the network subscriber having the master function to the network subscriber is identified if the network subscriber having the master function does not receive any acknowledgement of the start signal by the corresponding network subscriber.
A fault cause can thus advantageously be located.
In a further embodiment of the invention method, a network subscriber sends a fault-tracing signal, which characterizes this network subscriber, via the communication line if it has not received any initialization signal via the optical network line, wherein the network subscriber having the master function identifies a fault which relates to the transmission of an optical signal from the network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line is arranged upstream of that network subscriber which has sent a fault-tracing signal and which, in the transmission direction of the ring optical network line is arranged closest to the network subscriber having the master function, or which relates to reception of an optical signal by the network subscriber which sent the fault-tracing signal and which, in the transmission direction of the ring optical network line, is arranged closest to the network subscriber having the master function, or which relates to the ring optical network line between that network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line, is arranged. upstream of that network subscriber which sent the fault-tracing signal and which, in the transmission direction of the ring optical network line, is arranged closest to the network subscriber having the master function, and to this same network subscriber which sent the fault-tracing signal and, in the transmission direction of the ring optical network line, is arranged closest to the network subscriber having the master function.
In this case, for fault tracing, it must be remembered that the optical signals run around a ring. Thus, if no signal arrives at one network subscriber, this network subscriber cannot pass on any signal either. Thus where the fault-tracing signals of the individual subscribers are sent via the communication line, the network subscriber having the master function will receive fault-tracing signals from all those network subscribers which are located downstream of the fault location in the transmission direction of the ring optical network line. For systematic fault tracing purposes, therefore, the first fault to be rectified in this case would therefore be that which was observed in the network subscriber which, in the transmission direction of the ring optical network line, is arranged closest to the network subscriber having the master function. Another test procedure can be carried out once this fault has been rectified. The other fault entries may arise only from the fact that it has not been possible for a network subscriber to pass on any signals since this subscriber has not been able to receive any signals. Thus, there need not be any further faults on the ring optical network line.
In the method according to claim 4, a network subscriber transmits a fault signal which characterizes this network subscriber, via the optical network line, if it has not received any initialization signal via the optical network line, wherein, on reception of this fault signal, the network subscriber having the master function identifies a fault which relates to the transmission of an optical signal by that network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line, is arranged upstream of that subscriber which sent a fault signal, or which relates to the reception of an optical signal by that network subscriber which sent the fault signal, or which relates to the ring optical network line between that network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line, is arranged upstream of that network subscriber which sent the fault signal, and the same network subscriber, wherein the network subscriber having the master function identifies a fault which relates to the transmission of an optical signal by that network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line, is arranged upstream of the network subscriber having the master function, or which relates to reception of an optical signal by the network subscriber having the master function, or which relates to the ring optical network line between that network subscriber which, in the opposite direction to the transmission direction of the signal in the ring optical network line, is arranged upstream of the network subscriber having the master function, and the same network subscriber, if the network subscriber having the master function does not receive a fault signal. Thus, the location of a fault is found by transmitting a signal via the ring optical network line. In some circumstances, it is possible for signal transmission through the ring optical network line to be interrupted at more than one point. In this case, since the fault signal is transmitted via the ring optical network line, a fault is initially identified at that point which, in the opposite direction to the transmission direction in the ring optical network line, is the closest to the network subscriber having the master function. Once this fault has been rectified, it is then possible to look for other faults which may be present.
According to on embodiment of the invention method, the respective network subscriber can use various criteria to identify the fact that it has not received any initialization signals. Firstly, time criteria may be defined for this purpose in such a way that a network subscriber identifies the fact that it is not received any initialization signal if no initialization signal has been received by this network subscriber once a specific time threshold has passed since the network subscriber received the start signal via the communication line. It is also possible for the network subscriber having the master function to transmit a fault acknowledgement signal via the communication line, if the network subscriber having the master function has not received any signal via the ring optical network line, or has received only a signal which does not correspond to the nominal signal, within a specific time threshold.
In another embodiment of the invention, a test set can be used to replace the function of a receiver or a transmitter of a network subscriber in the start and initialization phase.
In another embodiment of the invention, a test set can be used to replace the function of a network subscriber, with the respective associated receiver and transmitter, in the start and initialization phase.
In the method just described, individual components can advantageously be replaced, for the purpose of systematic fault tracing, once the location of the fault has been found. Since the test is then repeated, it is possible to check whether the network is functioning after the replacement has been carried out. In this way, faulty components can be determined.
Since the functional scope of the test set is reduced in comparison to normal operation of the network, the logistics complexity can advantageously be minimized, since one test set may be used to replace the network subscribers in the test phase.